Wetland drainage and streamflow trends in Illinois

Long-term streamflow records from 30 gaging stations in Illinois were analyzed to assess the impact of wetland drainage on streamflow trends. The objective of the research was to determine any detectable trends, either increasing or decreasing, in streamflow parameters that can be attributed to wetland drainage. The analysis shows that most of the stations show increasing trends for annual daily mean flow and annual daily peakflow. At the same time, however, daily peak precipitation also shows increasing trends. The ratio between daily peakflow and daily peak precipitation shows increasing trends for 52% of the stations. Increasing trends for the ratio between peakflow and peak precipitation are found for 70% of the stations in southern Illinois and 50% of the stations in central Illinois, whereas only 33% of the stations in northern Illinois show increasing trends. Low-flow analysis indicates that low flows show increasing trends for 88% of the stations analyzed.